Attention is recently paid to application management configuration called a cloud and utilizing an information system not maintained by its own organization but provided by another organization so as to enhance the efficiency of management expenses for the development and the application of the information system. In the meantime, since an organization that manages the information system is different from an organization that utilizes the information system in the cloud, it is difficult to take measures to prevent information leakage and others, to find a cause after the occurrence of an accident, and to prevent recurrence in only its own organization. Therefore, for measures to prevent an unjust outflow of data beforehand, encrypting technique is required to be utilized and the confidentiality of data is required to be secured.
In the server/client model, for technique for preventing the leakage of data deposited in a server while a client deposits data in the server, a method utilizing encryption technique is known. For example, in Dawn Xiaodong Song, David Wagner, Arian Perrig. “Practical Techniques for Searches on Encrypted Data”, In Proceedings of the 2000 IEEE Symposium on Security and Privacy, pages 44-55 (2000) and JP-A No. 2012-123614, a method of searching deposited encrypted data without decrypting the encrypted data according to a request of a client is described. In this search method, a stochastic encryption system which is more secure than a definite encryption system having the one-to-one simple correlation of unciphered text and ciphertext and which has the one-to-m complex correlation of unciphered text and ciphertext is adopted, and techniques for securely searching data deposited in a server while preventing information leakage to a server manager are disclosed.